<em>In-situ</em> dynamic activation promotes the synergy between adsorbate evolution and lattice oxygen mechanisms for efficient water oxidation

The synergistic activation of metal and lattice oxygen in transition metal-based catalysts through adsorbate evolution mechanism (AEM) and lattice oxygen mechanism (LOM) is regarded as one of the key strategies for boosting oxygen evolution reaction (OER) activity and stability, but still remains challenge. Herein, leveraging an <em>in-situ</em> electrochemical activation, we reveal that the designed bimetallic phosphide heterojunction is dynamically activated into coexisting phosphides and hydroxides active phases, each following the AEM and LOM pathways respectively. Specifically, Ni atoms at the dense NiFeP@FeP heterointerfaces effectively tune the RDS (OH* to O* ) energy barrier under the AEM pathway, while the interface interaction in NiFeP-NiFe LDH weakens the metal-O bond and lowers the d-band center of metal sites, enabling effective LOM pathway. <em>In-situ </em>spectroscopy combined with ¹⁸O-isotopic labelling and differential electrochemical mass spectrometry (DEMS) measurements revealed dynamic reconfiguration and both involved adsorbed/lattice oxygen signature products in the oxygen release process, affirming the synergy of AEM-LOM pathway. As a result, the activated catalyst only requires overpotentials of 197/233 mV to drive current densities of 10/100 mA cm⁻², accompanied by Tafel slope of 32 mV dec^-1 and TOF value of 0.05 s^-1, as well as high stability for OER. This work provides insights for deeper understanding of the OER mechanism of transition metal phosphides and the design of high efficient catalysts.